1. Field of the Invention
The present invention relates to a line pattern formation method using a liquid material containing a pattern formation material dispersed or dissolved therein, a device and an electronic apparatus (electronic machine).
2. Description of the Related Art
Conventionally, techniques, such as a photolithography method, a transfer method, a mask printing method, and a plating method, were used to produce circuit patterns of printed circuit boards. In recent years, attention was given to a technique for directly printing a pattern on a substrate using an electronically-conductive microparticle paste, which contains electronically conductive microparticles dispersed therein, by using an inkjet method.
However, ink that is used in the inkjet method has low viscosity so that the ink can be ejected, and such ink tends to spread widely. Therefore, it has been difficult to draw a thin circuit pattern by using the inkjet method. Further, in the inkjet method, a so-called coffee stain effect occurs because the speed of evaporation of liquid at a rim portion of the liquid and the speed of evaporation of the liquid at a central portion of the liquid are not the same. Particles accumulate in the rim portion, and there is a problem that when the ink dries, the thickness of the layer in the rim portion and the thickness of the layer in the central portion are not the same. Therefore, a layer formation method for preventing the thickness of the layer from becoming uneven has been proposed (please refer to Japanese Unexamined Patent Publication No. 2003-318516).
The method disclosed in Japanese Unexamined Patent Publication No. 2003-318516 includes a first ejection step for forming a line pattern by dropping liquid droplets of a liquid material containing a layer formation component therein onto a substrate, a drying step for drying the line pattern, and a second ejection step for dropping liquid droplets onto a depression on a dried body that has been formed on the substrate in the drying step. As described above, in the method disclosed in Japanese Unexamined Patent Publication No. 2003-318516, the drying step that promotes the coffee stain effect is provided after a line pattern is formed in the first ejection step to intentionally generate a height difference (a difference between a thick portion and a thin portion) in the dried body. Consequently, a depression is formed on the dried body. Further, in the second ejection step, liquid droplets are further dropped into the depression. Accordingly, it is possible to make the thickness of the line pattern even.
Meanwhile, when a coating (coating layer) is formed by using an inkjet method, a method for forming a flat coating is proposed (please refer to Japanese Unexamined Patent Publication No. 2004-016916). In the method, after a coating is formed in a first ejection step, a certain amount of liquid that can fill a depression formed in the coating is dropped into the depression in a second ejection step to form a flat coating (please refer to Japanese Unexamined Patent Publication No. 2004-016916).
However, in the method disclosed in Japanese Unexamined Patent Publication No. 2003-318516, when the depression formed in the dried body by the first ejection step and the drying step is small, if droplets of liquid are dropped at an appropriate dot pitch for forming a line pattern in the second ejection step, the volume of the dropped droplets of liquid is greater than the volume of the depression. Therefore, when the droplets of liquid dropped into the depression in the dried body dry, a line pattern having a projected cross-section is formed. In this case, the ejection pitch in the second ejection step may be set longer than an appropriate ejection pitch for forming the line pattern so that the droplets of liquid are less densely ejected. However, when the droplets of liquid are less densely ejected, jaggies are generated, and an even line pattern is not formed. Further, when the formed line pattern does not have an even thickness, the risk of disconnection of circuits by unevenness in the density of electric current increases in the formed line pattern.
Meanwhile, in the method disclosed in Japanese Unexamined Patent Publication No. 2004-016916, in formation of the coating, the amount of the droplets of liquid ejected in the second ejection step is controlled so that the depression in the coating formed in the first ejection step is filled. Therefore, it is impossible to apply the method disclosed in Japanese Unexamined Patent Publication No. 2004-16916 to formation a line pattern.